Improve queueing and locking of builds exposed to runners [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This merge request introduced a limit to the builds queue depth. This will limit the amount of builds we go through to find a build that can be picked by runners. Should also reduce the number of 409 responses by making it less like to fall into the Triangular Requests problem with GitLab Runners.

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines

Issues

• #292047 (closed)
• #118495 (closed)